Sound system



March 15, 1966 KANESUKE Klsl-n SOUND SYSTEM 5 Sheets-Sheet l Filed OGb. 2l, 1964 .Zi-1.2511751? f/(czneSu/(e 'S/LL' @v/W March 15, 1966 KANESUKE Klsl-n 3,240,289

I SOUND SYSTEM Filed Oct. 21, 1964 3 Sheets-Sheet 2 Inzenf'ar ATTI-Lys.

March 15, 1955 KANESUKE KlsHl SOUND SYSTEM 3 Sheets-Sheet .f3

Filed Oct. 21, 1964 United States Patent 3,240,289 SOUND SYSTEM Kanesuke Kishi, Kawasaki-shi, Japan, assignor to Sony Corporation, Tokyo, Japan, a corporation of Japan Filed Oct. 21, 1964, Ser. No. 405,402 Claims priority, application Japan, Oct. 25, 1963, 38/57,0S1 7 Claims. (Cl. 181-31) This invention relates to a sound system and more particularly to a sound system wherein a relatively small speaker enclosur-e will produce greatly improved low fre quency response.

Relatively small speaker enclosures usually employ a cone-type speaker. It is well known that the response of a cone-type speaker is attenuated significantly in the low frequency region. This attenuation is due to a source established at the diaphragm composed of two sound wave components having d-iametrically opposed phase relationship, the cumulative effect of which is mutual cancellation and a resulting void in the frequency spectrum. l

Attempts have been made in the past to compensate for this low frequency failure but these attempts have inevitably resulted in the use of Irelatively large-size cabinets. For example, the radius of a bafiie board employed for this purpose would be determined from the equation Rb--C/lfc where C is the velocity of sound and fc is the low frequency cut off. If fc is to be in the neighborhood of 100 cycles per second, the baffle board required would have to have a diameter of approximately 1.8 meters. Small transistor radio casings are only a small fraction of this dimension and a bathe board for such or the equivalent thereof might have an effective radius of 15 cm. Such a device, however, would have a cut-off frequency of approximately 600 cycles per second, and' would therefore have very poor delity. The primary object of this invention is to achieve a more nearly uniform frequency response from a sound system without enlarging its overall dimensions. In particular, this invent-ion is directed toward improving the low frequency res-ponse of small size devices.

. kIt is also an object of the present invention to provide a small speaker cabinet which utilizes sub-diaphragms to maintain a hig-h radiation eiiiciency, the term sub-diaphragm being used herein to identify a secondary or subsidiary diaphragm which is not directly excited by an electrical means but rather a diaphragm which is excited in the sound system by variations in air pressure.

It is a more lspecific object of this .invention to provide a speaker cabinet having sub-diaphragms forming the side walls or portions of the side walls thereof, and having relatively rigid back and front panels.

Further features, objects and advantages encompassing this invention will become apparent from the following references to the accompanying drawings in which certain preferred embodiments are shown:

FIGUREl is a diagrammatic view of a sound system embodying the present invention with an accompanying vector diagram representing a feature of its operation;

FIGURE 2 is a perspective view of a sound system constructed in accordance with the teachings of the present invention including the speaker enclosure and the principal speaker;

FIGURE 3 is a perspective view of the sound system of FIGURE 2 but with the principal speaker assembled in its enclosure;

FIGURE 4 is a further perspective view of a sound system shown in FIGURE 3 but being principally a front elevational view; n

FIG-URE 5 is a sectional view taken along the line Patented Mar. 15, 1966 A-A of FIGURE 4 and FIGURE 5A is an enlarged fragmentary section of a portion of FIGURE 5;

FIGURE 6 is a front elevational View of the same sound system;

FIGURE 7 is a graph displaying the frequency response of a top sub-diaphragm and one side su-bdiaphrag-m employed in the sound system illustrated 1n FIGURES 1 to 6 of the drawings;

FIGURE 8 is a graph displaying the frequency response of this same sound system under different envlronmental conditions;

FIGURE 9 is an electrical analog to the mechanical `aspects of the sound system illustrated in FIGURES l to 6 of the drawings; and

FIGURES 10, 11 and 12 are diagrammatic illustrations of different embodiments of the present invention.

In FIGURES 1 to 6 of the drawings there is illustrated a sound system including a speaker enclosure of cabinet 1 having a front wall 2, a rear wall 3 and four side walls 4, 5, 6 and 7. The front wall 2 has a central opening 8 therein in which is mounted a speaker 9 having a conetype diaphragm 10 and an electroacoustical transducer 11. In order to hereinafter discuss certain characteristic features and advantages of the present invention the sound system illustrated in FIGURE 1 may be considered to be one in which the cabinet 1 is dimensioned to be 13 x 13 x 8 cm. while the diameter of the speaker diaphragm 10 may be considered to be l0 cm. The inner volume of the cabinet 1 is approximately 1.170 cm.3

In the illustrated preferred embodiment of the present invention the front and rear panels 2 and 3 are formed of relatively rigid vinyl chloride plates having a thickness of approximately 4 mm. The side walls 4, 5, 6 and 7 are formed as sub-diaphragm panels by forming them of a plastic material such as vinyl chloride, polyethylene, propylene or the like in the form of a thin sheet or membrane of about l mm. thickness and having a low Q. It is -to be understood that the term Q represents the sharpness of the resonance. It has been found desirable to place a coating 12 of a synthetic rubber-type adhesive on the back of each such sub-diaphragm as a damping means. Such coating may be about 2 m-m. in thickness. The front and rear panels 2 and 3 are structurally secured together by brackets or cross bars 13, `It has been found that under some circumstances improved results can be p obtained by disposing an elastic member 14 formed of a material such as polyurethane between each of the subdiaphragms 4, 5, 6 and 7 and its adjacent bracket 13. The elastic member 14 is relativelysmall in cross-sec tional area and is centrally located in the sub-diaphragm against which it is disposed.

As is shown particularly in FIGURE 5, a small quantity of glass liber 15 is disposed over the inner surface of the rear wall 3 of the cabinet 1 in order that a standing wave may be established at a range higher than 1,000 cycles per second.

For reasons which will hereinafter be made evident it is important that the cabinet 1 with its associated speaker 9 be substantially air-tight.

In order to mo-re fully appreciate the present invention, certain distinctive characteristics of a cone-type speaker and its associated enclosure should be noted. In a con ventional enclosure, a normal sound wave radiated at the front lof a speaker cone has associated therewith a reverse sound wave having a velocity component in the direction of the principal axis of the cone which tends to cancel or attenuate substantially the normal sound wave. This reverse phase sound is caused by the leakage at the baffle board or cabinet or is due t'o a secondary sound wave radiated by the vibration of the front or rear panels of the enclosure. Thisreverse phase sound is, of course, undesirable in a sound system. I have noted that a sound wave having a velocity component in a direction at right angles to the principal axis of the speaker cone is an effective means of reinforcing the response of the system. The preferred embodiment of the invention, as shown in FIGURES 1 to 6 of the drawings, is achieved by the seconda-ry radiations coming from the side panel sub-diaphragms 4, 5, 6 and 7 excited by the inner pressure of the cabinet. Since the sub-diaphragms have a predetermined large mechanical compliance, there is substantially no phase difference between the secondary radiation and the inner pressure. These sub-diaphragms 4, 5, 6 and 7 are chosen to be resonant in the low frequency area of interest with a low value of Q rendering a broad region of reinforced response as indicated by FIGURE 7. As a result of this a-rrangement, in this low frequency region, an intensified composite sound wave is obtained giving increased fidelity to the total system response.

FIGURE 7 shows frequency response characteristics for two of the four sub-diaphragms found in the sound system of FIGURES 1 to 6 and specifically relates to those found in sub-diaphragm panels 4 and 5. When a sound system was tested having the dimensions and characteristics described in connection with FIGURES l to 6, the sub-diaphragms were found to have a resonant peak at approximately 500 cycles per second and the value of Q was adjusted between 2 and 3. In FIGURE 7 the full line curve 11 represents the response characteristic for the sub-diaphragm 4 and the dotted line represents the response characteristic for the sub-diaphragm 5. It will be noted that in both instances the response remains strong for values of frequency below and above resonance.

It will further be noted that the region of highest response is a region Where the normal response from small sound systems of the past have little or no response. This can be utilized to give an overall sound system response which is relatively uniform to a point somewhere below 200 cycles per second, as is evident from an examination of FIGURE 8.

FIGURE 8 of the drawing illustrates the total -response of the sound system of FIGURES l to 6 under varying environmental conditions. In one situation the sound system was mounted in a room in which there was substantially no reflection. The full line curve 18 of FIG- URE 8 represents the response under this situation. Another environmental condition was arranged for the sound system in which the sound system cabinet 1 was mounted with its back wall directly against the wall of a room having normal sound reflection characteristics. The overall response of such a system is represented by the broken line 19 of FIGURE 8. The third situation was to mount the cabinet 1 of the sound system in the corner of an ordinary poom, and the averall response from such an arrangement is represented by the dash-dot line 20 of FIGURE 8. A fourth environmental situation was arranged by placing the cabinet 1 against one wall of an ordinary room but close to a corner thereof so that one sub-diaphragm was spaced fnom `but close to the wall adjacent the first wall of the room. The overall response of the sound system under this condition is represented by the dotted line 21 of FIGURE 8. In all cases, great improvement is found in the low frequency response. It will be noted that with a cone speaker and cabinet of the same size but without sub-diaphragms, the low frequency cut-off is around 600 cycles per second. With the present invention this cut-off point is lowered materially without increasing the size of the enclosure.

A still further improvement results by utilizing the reection characteristics of the noom or space in which the system is disposed. This could be a room, a compartment in an airplane or automobile and the like.

FIGURE 8 demonstrates that the low frequency response of a sound system constructed in accordance with the teachings of the present invention can be further improved by utilizing environmental reiiections. The arrangement represented by the dotted line 21 represents approximately a 10 db improvement in the low frequency region concerned over the situation found in a nonreflecting room. From this fact it will be readily observed that the ordinarily confined environmental conditions characteristically found in automobiles, ships and planes can be an effective means of increasing the overall system response,

The sound system of the present invention will be better understood by a consideration of the electrical analog thereof as illustrated in FIGURE 9. The acoustical impedance of the cabinet Zc is represented as the summation of the acoustical compliance of the cabinet in parallel combination with the sub-diaphragm impedance consisting of mass Ms, mechanical compliance Cs, and a mechanical resistance Rs. Zc is connected in ser-ies with the principal diaphragm impedance Mo, Co and R0. The input of the circuit is a voltage source and is comparable to the force applied to the principal diaphragm through the electromechanical transducer.

It is well understood by those acquainted with electrical circuit theory that the impedance of a parallel combination is always less than the impedance of either branch. Therefore, regardless of the values of MS, Cs and Rs, Zc will always be lessened by the presence of the diapraghm factors. However, when [Rs-t-KwMs-l/C'Ql is less than or equal to 1/ jwCa the sub-diaphragms become an effective by-pass to Ca with the result that Zc is significantly reduced. Since Ca is a cabinet volume dependent factor, it is recognized that the shunt effect of the subdiaphragm is to permit a decrease in cabinet volume without causing a corresponding increase in ZC. If the response of the sound system is likened to the current in the circuit, a diminished Zc will result in a stronger cornparative response for the frequency range in which the sub-diaphragm experiences lowest impedance. This is the frequency range centered at resonance which as shown in FIGURE 4 is approximately 500 cycles per second.

Experiments have shown that the volume reducing effect of the sub-diaphragm shunt path is between 50 to 70%. In particular, the cabinet of FIGURE 1 having a volume of about 1,170 cm3. has a response equivalent in fidelity to a conventional cabinet having a volume exceeding 2,000 cm3.

FIGURES 10, 1l and 12 illustrate modified forms of the present invention. In FIGURE 10, the side panel sub-diaphragms are replaced by drone cones 22, 23, 24 and 25. The main speaker 10, however, remains the same. The front wall 2 and the back wall (not shown in FIGURE 10) remain relatively rigid. The side walls 26 in which the cones 22 to 25 are mounted are also relatively rigid. The cones 22 to 25 have a natural resonant period of mechanical vibration at around 500 cycles per second.

In the forms of the invention shown in FIGURES 11 and 12, the front and rear walls are made of relatively rigid material and are disposed in spaced parallel relationship. The connecting wall between the front and rear panels forms a sub-diaphragm 27 which is circular in cross-sectional configuration in the form of the invention shown in FIGURE 11 and is elliptical in cross-sectional configuration in the form of the invention shown in FIG- URE 12. These sub-diaphragm connecting panels are designed to have a resonant period of mechanical vibration at around 500 cycles.

In the form of the invention shown in FIGURE l2 two principal speakers 28 and 29 are provided which are electrically driven.

In each form of the invention shown in FIGURES 10, 11 and 12 the enclosure is made substantially air-tight.

The materials given in the illustrated embodiments of the invention are given by way of example and not by way of limitation, it being desirable only that the front and rear panels of the sound system be relatively rigid and that the sub-diaphragms be formed, dimensioned and mounted in such a Way as to have a natural mechanical resonant frequency somewhat below the normal cut-oil frequency of the principal speaker alone. It is further important that the sub-diaphragms be disposed so as to vibrate substantially at right angles to the axis of vibration of the principal speaker or speakers.

It Will be understood that modifications and variations may be effected without departing from the scope of the novel concepts ofthe present invention.

I claim as my invention:

1. An enclosure for a cone speaker comprising:

(a) a rigid front wall having an opening for receiving the speaker therein,

(b) a rigid back wall, and

(c) a plurality of said Walls formed entirely of a thin membrane and each defining a subdiaphragm panel and positioned parallel to an axis of the opening in said rigid front wall.

2. An enclosure for a cone speaker comprising:

(a) a rigid front wall having an opening for receiving the speaker therein,

(b) a rigid back wall spaced from said front wall and parallel thereto, and

(c) a plurality of said walls extending between said front and said back Wall and formed entirely of a thin membrane, each of said side walls defining a sub-diaphragm panel and positioned parallel to an axis of the opening in said front wall.

3. An enclosure for a cone speaker comprising:

(a) a rigid front wall having an opening for receiving the speaker therein,

(b) a rigid back Wall,

(c) a plurality of side Walls formed entirely of a thin membrane and each dening a sub-diaphragm panel and positoned parallel to an axis of the opening in said rigid front Wall, and

(d) a damping layer secured to an inner face of each of said side walls.

4. The enclosure as delined in claim 3 wherein said damping layer is a synthetic rubber-type adhesive.

S. An enclosure for a cone speaker comprising:

(a) a rigid front Wall having an opening for receiving the speaker therein,

(b) a rigid back wall,

(c) a plurality of brackets extending between said front and said back wall, and

(d) a plurality of side walls formed entirely of a thin membrane and each dening a sub-diaphragm panel and positoned adjacent a respective one of said brackets and parallel to an axis of the opening in said rigid front wall.

6. An enclosure for a cone speaker comprising:

(a) a rigid front Wall having an opening for receiving the speaker therein,

(b) a rigid back Wall,

(e) a plurality of brackets extending between said front and said back wall, and

(d) a plurality of side walls formed entirely of a thin membrane and each dening a sub-diaphragm panel and positioned parallel to an axis of the opening in said rigid front wall, said side walls being outwardly spaced from said brackets to allow vibratory movement thereof.

7. The enclosure as defined in claim 6 including a plurality of elastic members positioned between a respective one of said brackets and a respective one of said side walls.

References Cited by the Examiner UNITED STATES PATENTS 1,787,946 1/1931 LaRue 181-31 X 1,988,250 1/1935 Olson 181-31 2,059,929 11/1936 Bobb 181-31 2,549,091 4/1951 Hopkins 181-32 2,646,853 7/1953 Pocock 181-31 3,082,839 3/1963 Whitcas 181-31 3,101,810 8/1963 Doschek 181-31 40 LEO SMILOW, Primary Examiner. 

1. AN ENCLOSURE FOR A CONE SPEAKER COMPRISING: (A) A RIGID FRONT WALL HAVING AN OPENING FOR RECEIVING THE SPEAKER THEREIN, (B) A RIGID BACK WALL, AND (C) A PLURALITY OF SAID WALLS FORMED ENTIRELY OF A THIN MEMBRANE AND EACH DEFINING A SUB-DIAPHRAGM PANEL AND POSITIONED PARALLEL TO AN AXIS OF THE OPENING IN SAID RIGID FRONT WALL. 